The present invention relates to a process for manufacturing demineralized bone matrix. More specifically, the present invention relates to a method for manufacturing demineralized bone matrix, which focuses on the preservation of native/intrinsic growth factors residing within the matrix while providing unique handling characteristics. The demineralized bone matrix will be used in promoting bone and cartilage repair and bone and cartilage growth and regeneration.
Approximately one million bone graft procedures are conducted each year throughout the world. About 500,000 of these procedures are conducted in the United States, and roughly 250,000 of the bone grafting procedures in the United States involve the spine. These bone graft and bone substitute products may include, for example, bone substitutes, bone dowels, demineralized bone matrix products, including putties, “platelet” helpers, and other allograft bone materials.
Injury to the cartilage of the knee joint is also a common orthopedic problem, affecting millions of people in the United States. Damaged articular cartilage does not normally regenerate itself. Current treatment for cartilage damage requires patients to undergo arthroscopic surgery to relieve their symptoms. If the cartilage cannot be repaired, and must be removed, the patient is likely to develop osteoarthritis, with possible need for further surgeries, including total knee replacement in severe cases.
The use of bone materials to promote bone healing after fracture, bone loss, infection, tumor, or other pathologic conditions is well known to those skilled in the art. Typically, bone grafting employs one of three modalities to promote bone healing. First, an autologous bone graft may be used. An autologous bone graft is derived from the recipient and is commonly taken from the iliac bone. Second, a bone allograft may be used which refers to a graft derived from a separate donor, usually within the same species. Finally, a bone graft substitute may be used that is naturally derived (e.g., from bone chips, granulated bone powder, and the like) or, in the alternative, synthetic or semi-synthetic products, generally in the form of putty and gel type of defect fillers, made up of allogeneic bone chips, granules, or bone powder, with or without carriers.
Autologous bone graft, sometimes referred to as an autograft (i.e., the patient's own bone), may be harvested to supply the needed bone to repair the defect. As appreciated by those skilled in the art, there are many advantages for using autologous bone in bone defect repair. For example, autologous bone is typically viscoelastic, osteoconductive, osteoinductive, and osteogenic (i.e., contains cells in its matrix that promote bone formation). In addition, an autologous bone graft avoids histocompatibility and infectious disease issues. Autologous bone, however, is limited in supply, is generally painful to the patient upon harvesting, and may lead to significant donor site morbidity (i.e., may require additional surgical incisions in the patient, may lead to surgical complications, blood loss and may cause additional patient discomfort, and may ultimately increase patient recovery time).
Allograft bone grafts are advantageous from the standpoint of being available in larger quantities compared to autologous bone grafts. However, allograft bone grafts may present disadvantages relating to histocompatibility issues (e.g., rejection by recipient immune system), the potential harboring of infectious agents, and may also include bone with poor malleable or mechanical characteristics (e.g., elasticity, compressibility, resiliency, and the like) due to high calcium and mineral content. Presently available bone graft substitutes developed by those skilled in the art usually have many of the same disadvantages as outlined above with regards to allograft bone grafts. Bone allograft or synthetic graft substitute products are generally formulated as putty and gel type fillers, designed to be inserted into dead space (s) between bone defects (i.e., defect or void fillers). Traditionally, bone graft substitutes may be made from allogeneic bone chips, granules, or bone powder, or synthetic materials with or without carrier compositions. Additionally, there are a few xenogeneic bone graft products available that are made from bovine bone, and the present invention may be adapted to use other sources of starting material, such as bovine material. Disadvantages are similar to that presented with allografts, including potential immune reaction to xenogeneic bone and infectious agents, including prions.
Another significant disadvantage of the currently available autograft, allograft, and bone substitute products of the prior art is that they are generally unable to resist loading forces and maintain their shape and structural integrity during surgical use for bone repair. To date, no solid, pre-shaped, flexible, elastic product (bone-derived or synthetic) that is able to resist loading forces, deform and then regain its shape and structural integrity is available for surgical use. These characteristics are essential for producing bone repair that closely mimics the normal bone condition in the absence of the bone defect.
In addition, bone graft materials and bone graft substitutes are known to have structural, mechanical and biological characteristics (e.g., lack of compressibility, lack of elasticity, and the like), which hinder their surgical placement, require relatively invasive surgical procedures, or sub-optimally promote bone growth.
Some bone allograft materials or synthetic composites, including ceramics and allograft bone material, have attempted to mimic certain autograft characteristics. For example, prior art ceramic bone graft substitutes, such as tri-calcium phosphate compounds, have osteoconductive activity (i.e., facilitates formation of bone trellis structure by promoting vascularization), but do not have osteoinductive activity (i.e., possess bone morphogenetic proteins that facilitate formation of bone by active recruitment of stem cells from surrounding tissue). Moreover, it has been found that ceramic bone graft substitutes of the prior art may be brittle or fail under forces of compression, torsion, bending, and/or tension.
Prior art bone graft substitutes, including demineralized cortical bone powder and recombinant human bone morphogenic protein (rhBMP), are typically osteoinductive. These bone graft substitutes, however, lack osteoconductive properties and generally have no macrostructure to encourage cell ingrowth and sufficiently resist the forces of compression, torsion, bending, and/or tension. Although larger sized traditional allograft bone products are osteoconductive and have some of the mechanical strength properties of bone, they are less osteoinductive due to their mineral content, cortical structure, and overall density. To date, no grafting material exists that can be deformed, for example compressed, torqued, and/or bent, which possess the mechanical properties to allow it to regain its original shape, structure, and size.
Demineralized cortical bone matrix (DBM) putties developed by those skilled in the art commonly include very small (e.g., micron-sized) particles of cortical allograft bone (e.g., demineralized, nondemineralized, or both) mixed with a carrier to produce a workable putty or gel in varying viscosities. Prior art bone substitute compounds (e.g., putties, gels, solutions, and the like) may be introduced into a bone defect with a spatula, syringe or by hand. Since these prior art bone substitute compounds are malleable, they generally deform to fit irregular spaces. However, since the active particles are typically micron-sized, bone substitute putties, gels, solutions, and the like may not resemble normal bone macroscopically and, in addition, may not contain normal pores, surfaces, spaces, and bone architecture. Moreover, the carriers used in prior art bone substitute compounds generally hold the micron-sized particles in suspension or in a colloid that tends to degrade with time, leaving the construct without normal bony macro-structure. For example, under in vivo conditions and in the presence of saline, blood, and/or blood serum, and during irrigation, many of these bone substitute compounds (e.g., putties, gels, solutions, and the like) break down, dissolve, or ooze out of the bone void at the time of surgery or within minutes or hours after their introduction into the bone defect. Even those prior art bone substitute compounds that do not dissolve in vivo do not resemble normal bone in macro-structure.
In addition, the bone substitute compounds of the prior art may not maintain the general mechanical properties (e.g., elasticity, flexibility, resistance to compression, tension, torsion, bending, or the like) normally attributed to bone. To this end, there are no bone substitute compounds available that can be compressed into a bone void or into a metallic, plastic, or composite implanted matrix with the ability to expand to fit that void and in the process of expansion regain its respective micro and macro shape and size through maintenance of its physical properties or memory.
Studies of demineralized bone products have shown a great variability in osteoinductive potential as measured by various bioassays, including the ALP assay, native/intrinsic BMP levels evaluated by extraction and ELISA assay, and in vivo measures of bone fusion. Factors contributing to this variability may include differences in processing techniques. Varied current practices of delipidification, demineralization and terminal sterilization of bone have the potential to significantly and negatively affect native growth factors contained within the bone matrix. Chemical processing of bone matrix with prolonged exposure to high concentrations of acid or high levels of gamma irradiation all reduce osteoinductive activity of the treated bone. Current practices include demineralization processes that monitor solution pH changes during acid exposure and utilize set concentrations and exposure times to acid. None of the current practices are optimized to preserve native growth factors associated with the bone matrix by reducing exposure to acid. In addition, there is structural variability within cancellous bone found at different sites within the body and between donors (i.e. variation in porosity and density). Such variations significantly affect delipidification and demineralization processing outcomes, even between cancellous bone blocks of the same size. Currently, most experts in the art believe cancellous bone to be only osteoconductive and not osteoinductive (Schwarz 1991, Arch Orthop Trauma Surg.) (Finkemeier 2002, J. Bone Joint Surg.). This perception is maintained by processing methods that remove, or render inactive, osteoinductive growth factors. The present invention produces a cancellous bone matrix with higher quantities of active growth factors than current art processes. One skilled in the art would recognize that a process that minimizes exposure of the bone matrix to potential damaging agents during processing, optimized to preserve native growth factor levels, would be a considerable advance in the field.
Ozone is a gas with known lethal effects on microorganisms and resultant sterilizing properties that are used extensively in the water and food industries. Ozone is a strong bactericide needing only a few micrograms per milliliter for kill of organisms including aerobic and anaerobic bacteria such as: Bacteroides, Campylobacter, Clostridium, Corynebacteria, Escherichia, Klebsiella, Legionella, Mycobacteria, Propriobacteria, Pseudomonas, Salmonella, Shigella, Staphylococcus, Streptococcus, Yersinia, and Mycobacteria. It is also effective against viruses, including Flaviviridae, Filoviridae, Hepnaviridae, Herpesviridae, Orthomyxoviridae, Retroviridae. Coronaviridae, Togaviridae, Rhabdoviridae, Bunyaviridae, Pramyxoviridae, and Poxviridae. Non-enveloped susceptible viral families include: Adenoviridae, Picornaviridae, Papillomaviridae, Caliciviridae, Astroviridae, and Reoviridae. Ozone neutralizes microorganisms via a spectrum of mechanisms. Most-studied is ozone oxidation of bacterial lipids and proteins found in bacterial cell membranes, and viral envelope lipids, phospholipids, cholesterols, and glycoproteins. Ozone is also toxic to mammalian cells although the mechanisms are not completely understood. Application of ozone in the process of creating demineralized bone matrix has the potential for several improvements over currently available bone products, including bioburden reduction, sterilization, whitening of the bone, delipidification, and making growth factors within the matrix more available.
To date, those skilled in the art have been unsuccessful in their attempts to overcome the above-identified disadvantages associated with known and available prior art bone substitute compounds. In particular, those skilled in the art have been unsuccessful in identifying and producing bone grafting materials that mimic certain normal bone characteristics by having improved malleable or mechanical properties. In this regard, there is a need in the art for a bone replacement and/or growth enhancement product that (1) precisely mimics normal bone architecture in order to serve as a conduit for vascular and cell immigration; (2) is malleable and elastic; and (3) resists compression, tension, torsion, and bending forces, without fracturing and when deformed has the ability to regain its original shape, structure and size. Therefore, as readily appreciated by those skilled in the art, novel demineralized bone matrices, compositions, and methods for promoting the repair of bone defects that address the disadvantages of the known prior art would be a significant advancement in the art. These matrices have clinical application not only for bone void healing and bone regeneration, but also for cartilage regeneration by providing scaffolding and growth factors to stimulate growth of new tissue in a cartilage defect.
In the presence of saline or body fluids, a bone graft compound that can be compressed to fill a void (in bone or cartilage), which does not dissolve or decompose, and which retains its macro-structure for days or weeks would be a significant advancement in the art. Moreover, demineralized cancellous bone matrices that are osteoinductive, osteoconductive, bioresorbable, biocompatible, substantially similar in structure to bone or cartilage, easy to use and which reduce patient morbidity, and are cost-effective to manufacture would also be a significant advancement in the field.
In addition, there is also a need in the art for demineralized bone matrices that can be used in association with progenitor cells that can be injected and infiltrated into its porous structure to allow attachment, differentiation, proliferation and ultimately function to regenerate new tissue when transplanted or to serve as a 3-D cell culture environment for research and drug screening.
Finally, demineralized bone matrix can also be utilized as a carrier for bioactive agents, attached to the matrix surface by way of a coating, injection or impregnation, designed to release active biologic growth factors or pharmacologic agents immediately or over time. This would be a further advancement over the known prior art.